Guide Eugene Twahilga leads treks into Volcanoes National Park in search of gorillas. Before approaching them, he growls quietly to avoid scaring them.

Rebecca DavisNPR

It's not easy shaking a bad reputation. Take the gorilla, for example: It's been saddled with a sketchy rep for as long as anyone can remember. Something along the lines of big, hairy, ferocious and superhuman in strength. A bit daunting, perhaps. And yet folks who work with and study gorillas say they are as much gentle as giant. I recently had the opportunity to find out for myself thanks to a trip organized by the International Reporting Project that took us to Rwanda.

More than half of the world's mountain gorillas live in the Virunga mountains of East Africa, a volcanic chain that straddles Uganda, the Democratic Republic of the Congo and Rwanda. For years, a chunk of the Virungas has been protected from poachers and farmers, so unlike much of the land in this area that's been cleared for crops, the Virungas are still covered by lush rain forests.

On the Rwanda side, the protected zone is called Volcanoes National Park. It's where I went to hook up with a guide and a small group of visitors for a trek into gorilla territory. Once a day, these guides are allowed to take a few people into the forest to see the gorillas. The day I went, we were told we'd be searching for a group called Hirwa, which means Lucky One. It was a special opportunity because the Hirwa group has a very rare quality among mountain gorillas — a set of twins.

We started out before sunrise one Sunday morning, and though we were prepared for rain, the skies were clear and a soft mist hovered over the peaks of the volcanoes that encircled us. As we started into the forest, our guide, Eugene Twahilga, called us over and issued a few warnings: It's OK to take pictures, but no flash; speak quietly; and if you become frightened, do not run away.

As Eugene told us with a big smile on his face, "The gorillas might think they should chase you."

Mountain gorillas are still on the endangered species list. There are other kinds of gorillas in the world, but there are only about 800 of this particular subspecies, with 480 of them living in the Virungas. According to a 2010 census, the population here has grown by 25 percent in the past decade, which is good news.

But they still face some serious challenges. Gorilla vets will tell you that top on that list is disease, and in particular diseases spread to the gorillas through contact with humans. Poachers are not such a problem for this particular population of gorillas, but animal traps set by locals are. They're meant to capture antelope, but gorillas can also get caught in them and die from their injuries or exposure.

Once we entered the forest, our bright day turned dark thanks to the thick stands of bamboo and tangle of vines all around us. As we walked up the trail, Eugene started to growl. It was a warm, rumbly vocalization that he uses to keep from startling the gorillas. And then, about 20 minutes after we entered the forest, we saw our first gorilla.

To hear what happened next, listen to the story by clicking on the audio link above.

Just saying the word gorilla conjures an image of something mighty and ferocious. After all, gorillas are imposing. They're the world's largest primates, some weighing as much as 500 pounds. NPR's Rebecca Davis recently traveled to the Virunga Mountains in East Africa where about half of the world's remaining mountain gorillas live and she found that these great primates and their young can be as gentle as they are giant.

REBECCA DAVIS, BYLINE: If you ever hope to have an audience with Rwanda's most famous citizens, you have to get up before sunrise, pack up your rain gear, put on hiking boots, grab a pair of gardening gloves and catch a ride. OK, we're in the Land Cruisers and we are heading up the mountain. This is a volcanic mountain range that spreads across three countries - Uganda, Democratic Republic of the Congo and Rwanda.

I'm with a group of about 12 other visitors and our drivers let us out at the base of a trail that we're supposed to follow.

It's damp, but not too muddy and in front of us are the peaks of volcanoes. Today, we're going to see a group of gorillas in which there are a set of twins, so we're all pretty excited about seeing them. Twins, you see, are extremely rare among mountain gorillas. The ones we hope to catch up with are boys born into a group they've called Hirwa, which means Lucky One.

EUGENE TWAHILGA: Can you come closer down here please? Because now we enter the forest.

DAVIS: We lean in and our guide Eugene Twahilga says, keep close together. And when we do meet up with the gorillas, try to keep about 20 feet away from them. It's OK to take pictures, but no flash.

TWAHILGA: The flash is not normally allowed because seeing this flash might frighten the gorillas.

DAVIS: Can I ask you a quick question? We hear things like do look them in the eye, don't look them in the eye, turn your back, don't turn your back, run, don't run. Can you give us any advice?

TWAHILGA: Any advice? For these gorillas, you will never run. Does no good otherwise. You can do any other things, but don't try to run away.

DAVIS: Or they'll chase you. We laughed nervously. One of the silverbacks, the big daddy of the group, weighs in at 430 pounds. For years now, these forests and their inhabitants have been protected from poachers and farmers. So unlike much of the land in Rwanda that has been cleared for crops, the mountainsides here are still covered by rainforests. If you go to Google Earth and look up Volcanoes National Park, you'll see that this protected zone is like a small toupee on a bald man's head.

Yes, it is lush, but space is limited.

TWAHILGA: This bamboo is their favorite food. Before they eat it, they have to peel it first.

DAVIS: Eugene's been a guide for 13 years so he's come to know the gorillas and their habits as well as anyone. But a few years ago, on a trek with some tourists, he saw something he'd never seen before.

TWAHILGA: I was with a group and it was around 9:30 like that, we were watching the gorillas.

DAVIS: He says the gorillas were sitting around in an open area, munching and resting when suddenly a pregnant female stands up and walks away from the others.

TWAHILGA: And then, we saw that the females, like the other females, went down to the other female and then they surrounded the pregnant female.

DAVIS: With all the females forming a circle, Eugene says he could no longer see the pregnant gorilla, but suddenly, he heard a piercing noise, a cry.

TWAHILGA: That noise, I've never heard it again. Sounds like it was a bit painful.

DAVIS: Painful, yeah. Then, the male of the group, the silverback, began beating his chest. And Eugene says the female breaks through the circle and walks into a clearing carrying a newborn baby on her arm.

TWAHILGA: Yeah, that was a good experience. So they were very happy, because it's not everybody who can see that.

DAVIS: Especially since mountain gorillas give birth only once every four years, so the population grows slowly. But the most recent census shows the number of the gorillas in the Virungas has grown by 25 percent in the last decade. Today, there are about 480 mountain gorillas living in these forests.

But make no mistake, they face some serious challenges. Top on that list is the threat of disease, especially diseases from people coming into contact with the gorillas. Since these primates are so much like us, human viruses spread easily and dangerously among them.

There's also pressures on the gorilla habitat from locals who venture into the forest for wood and to set traps for antelope - traps which also injure and kill gorillas. And then there's the political instability and fighting in parts of this region, which means gunfire and more disruption to these forests and the animal life that lives here.

TWAHILGA: Need a hand?

DAVIS: Grab my fingers.

And now we're in a stand of bamboo totally enclosed over our heads. It's dark and we've been advised to speak quietly.

(SOUNDBITE OF GROWLING)

DAVIS: I hear a growling sound. What is that? It's our guide letting the gorillas know that we're here so we don't startle them. That's very nice of him. I'm not sure I want to meet a startled gorilla.

DAVIS: The twins are playing. They're absolutely adorable. And they're kind of about the size of a toddler. And they're rolling around on their mom's belly. They're still nursing. Oh, one just started beating on his chest and sort of fell over. I'd say that was a juvenile. The baby's coming our way. They don't want us getting that close to the baby or any of the gorillas. Yep, we're backing up.

DAVIS: Yep. So we're back lying down. I have to say when he got up and started moving, I started to feel a little nervous. May I remind you, these things are huge and he's just lying there. It's crazy. Like he's reclining, looking at us.

Are they always this mellow?

TWAHILGA: Mm, it depends, because every morning after they wake up they start to eat. They eat intensively and then around this time then they have their first break.

(SOUNDBITE OF GROWLING)

DAVIS: And for the better part of an hour we stood there watching this little country scene: sun breaking through the trees; an afternoon nap. A cheeky toddler annoying its dozing mother. And if it hadn't been for the clutter of vines and bamboo, we would've spread a blanket and been lulled into a gentle sleep among the gorillas.

(SOUNDBITE OF MUSIC)

SIMON: Rebecca Davis traveled to Rwanda on a program organized by the International Reporting Project.